Significance This study is necessary to conduct prior to the start of human clinical trials, in a non-human primate that is closely related physiologically to humans. The application of this drug will be as a post-coital contraceptive in women. Objectives The purpose of this study is to determine whether the metabolic profiles of LNG are altered due to the formulation of LNG received. LNG will be administered orally in either tablet, capsule or 70% ethanol/water vehicle at 0.75 mg to three groups of 5 monkeys respectively. Blood samples will be collected twice prior to treatment, then at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 48, 72 and 96 hours post treatment. In order to model the dosing regimen to that which will be used in women, the timing of dosing to at or near ovulation will be used in this study since this is the most appropriate time of usage in women seeking post-coital contraceptives. Results We have completed the treatments of 11 of the 15 monkeys. All blood samples will be processed for serum and assayed by enzyme immunoassay for LNG content. Future Directions Results will be reported to the Contraceptive Development Branch and used for design of human clinical trials. KEY WORDS levonorgestrel, pharmacokinetic, post-coital contraception, synthetic progestin FUNDING NIH Grant HD-6-3247